OK, THIS IS MY LAST ATTEMPT AT GETTING THROUGH TO YOU. My 2001 Mercury Sable LS Premium slams into gear when accelerating from standing still. The local FLM dealer has replaced two transmission mount isolators without solving the problem. The car has just over 50k on the oddometer. What causes the problem and what's the remedy?

Optional Information:
2001 Mercury Sable LS Premiu DURATECH V6 24

Already Tried:
Local FLM dealer unsuccessfully